One advantage of using a digital input for an audio amplifier is that the layout of the printed circuit board (PCB) between the inputs and the amplifier is less critical than when using analog inputs. A second advantage is that the digital to analog conversion is implemented at the amplifier side, rather than at an earlier stage, for example in an audio processor. This reduces the total system costs, because the processors for processing audio data are typically made using advanced CMOS technology (CMOS90 or smaller), in which technology the area required for analog signals is large compared to the same required area needed at the amplifier side.
A one-bit pulse density modulation (PDM) stream may originate from a one-bit sigma-delta converter, in an audio processor, which can be relatively inexpensive. A good example of a PDM stream is the direct stream digital (DSD) stream used in super audio applications (SACD). This stream is a 64 times over-sampled one-bit PDM stream.
The advantage of using such a stream is that interpolation and sigma delta modulation, which is required for Digital to Analog conversion, is done at the audio processor side. Such interpolation requires a large chip area if it is done in the amplifier.